Cellular structure

ABSTRACT

A cellular, honeycomb-like structure comprised of a plurality of elements in stacked or juxtaposed relation, and each having a pattern of corrugations. At least every other element is characterized by a plurality of pairs of sections of dissimilar length which each define a corrugation. The corrugations of adjacent elements internist to define closed, generally triangular cells. It is characteristic of the structure that the peaks or nodes of the corrugations of each element engage upon the internode portions or slopes of the corrugations of the adjacent element. During assembly this enables relative movement between the elements until internesting is achieved. It is also characteristic of the structure that each cell is defined by one complete internodal section and portions of a pair of internodal sections of two adjoining elements. Various configurations of the structure for various purposes are disclosed.

June 13, 1972 c. K. FREDERICKS CELLULAR STRUCTURE Filed June 19, 1970 INVE N TOR. 0424 If. EewQe/c/(s June 13, 1972 c. K. FREDERICKS CELLULARSTRUCTURE 7 Sheets-Shes? 4.

Filed June 19, 1970 INVENTOR. 0424 I6 Fee-052mm;

FIGJZ June 13, 1972 K. FREDERICKS 3,669,820

CELLULAR STRUCTURE Filed June 19, 1970 7 Sheets-Sheet 6 F G I 9 IINVENTOR.

flrraewsns' June 13, 1972 c. K. FREDERICKS CELLULAR STRUCTURE 7Sheets-Sheet 7 Filed June 19, 1970 F I G. 20

FIG.2|

INVENTOR. 62424 A. FEEDER/CV65 BY wan 1% ATTOIQNEYS FIG.22

United States Patent'O I 3,669,820 I CELLULAR STRUCTURE v Carl K.Fredericks, San Diego, Calif., assignor to Corlite a Corporation, SanDiego, Calif. Continuation-impart of application Ser. No. 865,087, Oct.9, 1969. This application June 19, 1970, Ser.

r 1 Int. Cl. B32b 3/12, 3/28 I U.S. Cl. 16168 12 Claims ABSTRACT OF THEDISCLOSURE A cellular, honeycomb-like structure comprised ofv aplurality of elements in stacked or juxtaposed relation, and each havinga pattern of corrugations. At least every other element ischaracterizedby a plurality of pairs of sections of dissimilar length which eachdefine a corrugation. The corrugations of adjacent elements internest todefine closed, generally triangular cells. It is characteristic of thestructure that the peaks or nodes of the corrugations of each elementengage upon the internode portions or slopes of the corrugations of theadjacent element. During assembly this enables relative movement betweenthe elements until internesting is achieved. It is also characteristicof the structure that each cell is defined by one complete internodalsection and portions of a pair of internodal sections of two adjoiningelements. Various configurations of the structure for various purposesare disclosed.

ORQSS-REFERENCE TO RELATED APPLHCArTION :This is a continuation-impartofUS. patent application Ser. -No. 865,087, filed Oct. 9, 1969, nowabandoned and the benefit of the filing date thereof is claimed for thesubject matter which is common to that application and the presentapplication.

' BACKGROUND OF THE Field of the invention I Description of the priorart In the past, most conventional cellular, honeycomblike structureshave been fabricated in one of two ways. The first way involves theexpansion or pulling apart of a laminate of sheets of material bonded oradhered to gether at predetermined areas. More particularly, a fiatsheet of the material which is to form the cellular structure isprovided with a plurality of parallel, spaced apart stripes of adhesive.The subjacent sheet of material'is similarly provided with stripes ofadhesive, but with the stripes located intermediate the stripes of thesuperjacent sheet of material. This alternating pattern of stripes iscontinued throughout the stack of sheets, and the whole is bondedtogether. I

Next, the stack of bonded sheets is' opened in the manner of anaccordion to provide a plurality of hexagonal cells. This method suffersfrom various disadvantages. Since the cell wall sheet material must bedeformable at a stress lower than that required to fail the adhesivebond, thereby enabling the stack to be expanded, the strength andthickness of the cell walls is greatly limited. Thus, a cellularstructure having tiny cells of heavy gauge material cannot be produced.In addition, by virtue of 3,669,820 Patented June 13, 1972 the necessaryexpansion process involved, cellular structures made of resilientmaterial cannot be satisfactorily produced because of the tendency ofthe material to spring back, destroying the desired cell geometry.

Another method of the prior art involves the utilization of preformedelements which are arranged in complemental fashion to provide thedesired cell form, such as a hexagon form. Where a hexagonal cellpatternis desired, the complemental preformed elements forming thehalves of the cells must be veryv accurately aligned so that theirpoints of engagement or nodes are accurately located. This generallyrequires the utilization of mandrels located internally of the cellwalls, the mandrels also being utilized to provide the back-up structurewhich enables development of the pressures generally required at thenodes to effect proper bonding in the node areas. Avariation of thismethod utilizes a stack of alternate straight and corrugated elements toform triangularcells. However, a uniform cell array is very difiicult toachieve because of the problems inherent in aligning the nodes of thecorrugated elements.

The commonly practiced methods of theprior art involving hexagonal cellconfigurations also require that the securement or bonding betweenadjacent elements forming the cellular array be over an area. Such areacontact, as compared to line contact, requires double walls in the bondareas and, consequently, undesirable extra Weight.

Cellular structures of the prior art are primarily used as corematerials in so-called sandwich constructions. In that type ofconstruction the cellular core material is bonded or otherwise suitablysecured at its opposite surfaces to facing sheets or skins. These skinsstrengthen the assembly, particularly in bending. Without such facingskins the hexagonal cells of the cellular structure tend to flatten orcollapse when subjected to bending leads. Consequently, cellularstructures of the prior art could not be used in any long spans withoutfacing skins or auxiliary supports. This prevents their use indecorative applications, such as patio covers, where display of theircellular pattern is desired. The tendency of prior art cellularstructures to sag is typical of all non-triangular cell configurations,the lack of rigidity being occasioned by cell collapse or folding at thecell wall junctures or bend lines.

- SUMMARY According to the present invention, a cellular, honeycomb-likestructure is provided which is vastly different from either of thepreviously described structures of the prior art. However, it morenearly resembles the prior art structure which is formed by stacking orattaching a plurality of preformed elements in place, one on top of theother.

The present invention utilizes elements having corrugations configuredso that the nodes of the corrugations of each element engage upon theinternode or sloping portions of the adjacent elements and are movabletherealong during assembly to achieve a complete internesting. Moreparticularly, at least every other element is characterized by shortsections and long section s. Each short and long section joins or mergesto form a node, with the node and the adjacent short and long sectionsdefining one corrugation. The short and long sections thus constituteinternodal sections.

The elements are assembled, as by stacking them, so that the corrugationnodes of each element engage upon the internodal sections of itsneighbor elements. As will be more particularly described in thesubsequent disclosure, this enables the elements to be movedlongitudinally of one another during assembly. This in turn permits thenodes to move along the sloping, internodal sections until all of thenodes are properly engaged to"- effect complete internesting of theelements.

As will be seen, this arrangement provides a cellular structure in whichthe .cells are generally triangular in form, and in which the nodalsecurement or bond need only involve line contact with adjacentelements. In addition, because of the capability of relativelongitudinal movement inthe nodal areas, the stacked elements tend toautomatically position themselves properly with respect to one another.Consequently, only'moderate pressure upon the stacked elements is neededto effect proper internesting. This eliminates any need for mandrels oraccessory tooling to obtain alignment or to effect develop ment ofbonding pressure.

During assembly the end corrugations of the elements are constrainedagainst endwise'movement and flattening by suitable end restraints suchas plates or the like. In addition, the first or bottom element of thestacked ele ments is constrained against collapse or endwi se movementby a base plate or the like. By preserving the geometrical pattern ofthe bottom element the remaining elements are more easily aligned, aswill be seen. However, both the end restraints and the base plate can beeliminated in an alternative assembly precedure which utilizes aplurality of stacked doublets. A doublet is a pair of elements alreadysecured together to prevent endwise movement and flattening of theircorrugations. Stacked doublets are dimensionally stable and require onlyminimal pressure to achieve bonding therebetween. Use of stackeddoublets also greatly facilitates proper internesting of elements whichare made of flimsy, floppy materials, as will be seen.

With either of the foregoing arrangements, the preformed, stackedelements are automatically and accurately positioned so that adequate,positive pressure can be brought to bear against the nodal areas toachieve good bonds. By utilizing small radius nodes, the bond areas areessentially line bond areas or zones, thereby eliminat-' ing andtherefore can be made to span relatively large areas. However, the nodalareas can be of large radius configuration, if desired, to produce bondareas of greater area and strength.

The generally triangular configuration 'of the cells formed in thepresent structure provides greater stability against lateral celldeformation and greater rigidity, as compared to the well-knownhexagonal honeycomb cell structure. Consequently, the present cellularstructure can be used as a structural core material between facing skinsor sheets to provide a lightweight sandwich construction. However, byvirtue of the substantial rigidity provided by the triangular cellarray, which bears loads BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is aperspective view of an element forv use in forming the present cellularstructure, the element being characterized by a saw-tooth pattern;

FIG. 2 is an end elevational view of a plurality of stacked orjuxtaposed elements like the element of FIG. 1, alternate ones of saidelements being reversed in direction for interengagement or internestingin a predetermined pattern;

FIG. 3 is a perspective view of a doublet formed by securement togetherof a pair of the elements of FIG. 1, one of the elements being reversedin direction as compared to the other;

FIG. 4 is an end elevational view of a plurality of the doublets ofFIG-3 in stacked relation, the upper doublet being shown just prior toengagement with the lower doublet;

FIG. 5 is an end elevational view of a cellular structure in which theangular orientation of the legs or sides defining the corrugations issuch that the triangular cells,

are equilateral;

FIG. 6 is an end elevational view of a cellular structure in which theangular orientation of the legs orsides defining the corrugations issuch that the triangular cells are right angular with the acute anglesof each cell being similar;

FIG. 7 is an end elevational view of -a cellular structure in which theangular orientation of the legs or sides defining the corrugations issuch that the triangular cells are closerto right angular with the acuteangles of each cell being dissimilar;

FIG. 8 is an end elevational view of a cellular structure in which thedimensions of alternate ones of the stacked elements are dissimilar,thereby providing two sizes of cells in the array;

FIG. 9 is an end elevational view of a cellular structure in which thenodal areas are flattened to provide an increased area for securement orbonding between adjacent ones of the elements;

FIG. 10 is an end elevational view of a triplet, formed by assembly ofthree of the elements of FIG. 1; I FIG. 11 is an end elevational view ofa cylindrical container surrounded by the triplet of FIG; 10 in anenergy absorption application;

FIG. 12 is an end elevational view of a plurality of stacked orjuxtaposed elements having relatively large radius nodes which are notbonded, the structure being illustrated in an energy absorptionapplication;

FIG. 13 is an end elevational view of a cellular structurev in which theproximity of the corrugations of each element vary with respect to oneanother, thereby providing cells of increasing size in one direction;

'FIG. 14 is an end elevational view of a cellular structure in which thecorrugations of alternate elements are characterized by legs of equallength;

'FIG. 15 is a perspective view of another form of cellular structureaccording. to the invention, and in which the legs or sides of thecorrugations of alternate elements are inclined in two directionsrelative to the sides-of the corrugations of the adjacent elements;

FIG. 16 is a section taken along the line 16-16 of FIG. 15;

FIG. 17 is an end elevational view of a cellular structure in whichpermanently deformable elements are interleaved between alternate onesof a plurality of stacked elements, the'cellular structure beingillustrated in its undeformed state;

FIG. 18 is an end elevational view ofa pair of the elements of thestructure of FIG. 17, with one of the deformable elements interleavedtherebetween, and illustrating the structure in a deformed state;

FIG. 19 is an end elevational view of a cellular struc-' ture like thatof FIG. 12, but with certain of the nodes attached to adjacent elementsfor handling or the like while preserving its general capacity forenergy absorption;

FIG. 20 is an end elevational view of a pair of the elements of FIG.'12,with the addition of an undulating element and a straight element toimprove load dis tribution into the remainder of the structure withoutundesirable buckling of the outermost elements;

FIG. 21 is an end elevational view of the cellular structure of FIG. 12,but with alternate elements reversed and nested for shipment or thelike; and

FIG. 22 is an end elevational view of a cellular structure similar toFIG. 12, but illustrating a modified utilization of the energy absorbingelements.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings,and particularly to FIGS. 1 and 2, there is illustrated a cellularstructure 10 according to the present invention which comprises,generally, first and second elements 12 and 14 which are characterized,respectively, by a series of uniform waves or corrugations. Thecorrugations of element 12 are identical to each other, and thecorrugations of the element 14 are identical to each other. In thestructure 10 the corrugations of the elements 12 are also identical tothe corrugations of the elements 14. The structure 10 is an exemplaryembodiment of the invention and, as will be seen subsequently, otherembodiments of the invention differ in several respects.

Each corrugation of either the element 12 or the element 14 is definedby a succession of short and long sections 16 and 18, respectively,whose junctures define successive crests and valleys or nodes 20.

As best viewed in FIG. 2, the long sections 18 of the elements 12 aresimilarly directionally oriented, that is, they each slope downwardlyand to the right as viewed in the drawings. Of course, the termsdownwardly, upwardly, to the right or left, and crests and valleys arepurely relative terms and will vary according to the orientation of thecellular structure 10.

In contrast to the directional orientation of the long sections 18 ofthe elements 12, the long sections 18 of the elements 14 are oppositelyor reversely oriented so as to slope upwardly to the right, as viewed inFIG. 2, transversely of the long sections 18 of the adjacent elements12. This directional orientation is achieved by simply reversing thedirection or angularity of the alternate ones of the elements, that is,the elements 14 are reversely oriented with respect to the elements 12.

With this arrangement, the upper or alternate ones of the nodes 20 ofthe elements 14 engage successive long sections 18 of the superposed oradjacent element 12, while the lower or alternate ones of the nodes 20of the elements 12 engage successive ones of the long sections of theadjacent elements 14. This forms a plurality of generally triangularcells, each defined by a short section 16 and portions of a pair of theadjacent long sections 18.

The stacked elements 12 and 14 may be secured together in any suitablefashion, depending upon the material of which the elements are made andthe application for which the structure 10 is designed. For example, thematerial of the elements 12 and 14 can be made of resin reinforced glassfiber material, aluminum, magnesium, stainless steel, boron or graphitefilament reinforced materials, and suitable for load bearing ordecorative purposes. Securement of the elements 12 and 14 to one anothercan be effected by adhesively coating the nodes 20, and sometimes alsothe portions of the long sections 18 to which they are to be bonded, bywelding, brazing soldering, riveting, and various other techniques whichwill immediately-suggest themselves to those skilled in the art.

In one method of assembly, the elements 12 and 14 are made of thinaluminum foil which is provided with an adhesive stripe (not shown) uponthe nodes 20, with the elements 12 and 14 being stacked as shown in FIG.2. Since the thin foil may have a tendency to move laterally, the endsof the elements are constrained in any suitable fashion against suchmovement, such as by use of a pair of plates 22. In addition, the nodes20 of the bottom element 12 also have a tendency to move endwise orlaterally, and a saw-tooth configured base 24 is employed to preventthis. The elements are stacked above the base plate 24, with the bottomelement 12 nested in the plate 24 as illustrated. A platen 26 isarranged upon the uppermost of the elements and urged downwardly withsufficient pressure to generate adequate pressure at the nodes In FIG. 2the uppermost element 12 is shown just prior to being urged into contactwith the subjacent element 14.

It is an important feature of the present invention that the nodes 20of, for example, the elements 12 tend to slide upon the adjacent longsections 18 of the elements 14 until the nodes 20 of the elements 14 areproperly engaged with the long sections 18 of the elements 12. There isan automatic movement and alignment under the relatively light pressureof the platen 26. The sections, such as the short sections 16, tend toalign themselves exactly, one above the other, as seen in FIG. 2; Thisalignment and pressure is achieved without utilization of any mandrelsor the like disposed internally of the cells of the structure 10. As canbe seen from the drawings, this unique result is achieved in part byreason of the unequal lengths of the legs or sections 16 and 18, as wellas by reason of the orientation of the elements 14 relative to theelements 12.

There is virtually no limit to the number of elements 12 and 14 whichcan be juxtaposed in the described relation, so that very largestructural sections can be produced. The length or depth of the cells isdetermined by the width of the elements 12 and 14 utilized.Alternatively, a structure 10 of relatively great depth can be produced,and later sawed or otherwise cut into sections having the cell length orthickness of structure 10 de- Sired.

To facilitate assembly of the elements 12 and 14, particularly where theelements 12 and 14 are formed of generally thin or flexible materialwhich tends to flatten out and destroy the desired shape of thecorrugations, a plurality of doublets 28 are utilized, as best seen inFIG. 3. The doublet 28 is comprised of a pair of elements 12 and 14secured or bonded in any suitable fashion. Such securement, asillustrated, prevents the elements 12 and 14 from moving laterallyrelative to one another. Consequently, a plurality of the doublets 28can be stacked upon one another, as best seen in FIG. 4, to provide acellular structure 30 comprised of -a plurality of secured togetherdoublets 28. In this arrangement utilization of end plates 22 isunnecessary, and only the platen 26 is needed to achieve the necessarybonding pressure at the nodes 20.

FIGS. 5, 6, and 7 illustrate several of a large number of differentconfigurations of cells, each providing its own distinctive set ofphysical properties and aesthetic qualities. The pattern or array of'FIG. 5 is achieved by utilizing short sections 16a disposedperpendicular to an imaginary plane 32 passing through alternate nodes20a of the associated one of the elements 12a or 14a, as the case maybe. In FIG. 5, the triangular cells are equilateral by arranging thelong sections 18a so as to dispose them at an included angle ofapproximately sixty degrees relative to the short sections 16a.

General similarity of certain elements of FIGS. 5, 6, 7, 10, 12, 13, 14,15 and 16 to the elements 12, 14, 16, 18 and 20 of FIGS. 1-4 is denotedby letter subscripts adjacent the numerals, as follows: FIG. 5 (a); FIG.6 (b); FIG. 7 (c); FIG. 10 (d); FIG. 12 (e); FIG. 13 (f); FIGS. 11 and14 (g); and FIGS. 15 and 16 In FIG. 6, the cellular structure ischaracterized by short sections 16b disposed substantially perpendicularto the imaginary plane 32, and is further characterized by a dispositionof the long sections 18b at an angle of approximately forty-five degreesto the short sections 16b.

In the cellular structure of FIG. 7, the short sections are arranged tointersect the imaginary plane 32 at an included angle of approximatelysixty degrees, while the long sections are arranged to intersect theshort sections 160 at an included angle of approximately one hundreddegrees.

FIG. 8 illustrates yet another form of cellular structure according tothe present invention, the dimensions of the long sections 36 and theshort section 34 of first elements 37 being smaller than those of thealternate or second elements 39. The dissimilar dimensions of theelements 37 and 39 provide two sizes of triangular cells, which rendersthe arrangement suitable for decorative applications.

The cellular structure of FIG. 9 is essentially identical to thecellular structure 10 of FIG. 2, except that the nodal areas 38 areflattened to provide area contact with the adjacent long sections 40, ascompared to the essentially line contact present in the structure 10 ofFIG. 2. The structure of FIG. 9 affords a larger area for securement orbonding of the adjacent cell elements.

The structure of FIG. 10 comprising a triplet 42 is formed by a pair ofelements 12d with a reversely oriented element 14d therebetween. Theelements are secured together at their nodes 20d and the resultingassembly is sufficiently flexible, particularly if made of paperboardcorrugated box material, for example, that it can be wrapped around acylinder 44, as viewed in FIG. '1l, to protect the cylinder or toprotect fragile contents of the cylinder.-

If desired, the corrugations of elements 12e and 14e may be formed withrounded nodes 50, as seen in FIG. 12, rather than the sharp angularnodes 20 of the structure 10 of FIG. 2. The nodes 50 are connected bysmoothly faired sections, as illustrated. Such sections normally arerelatively straight although they may be slightly cunvilinear, asillustrated, if desired.

If the elements 12e and 14e are made of relatively stiff material, theywill retain their corrugated shape of their own accord, without resortto an arrangement such as that of the doublets 28 to hold their shape. Aplurality of such relatively stiff elements 12e and 14e can beassembled, as shown in FIG. 12, without attaching the elements. at theirnodes 50. The elements are merely stacked upon one another, with theasembly being loosely held together by gravity.

Such a plurality of stacked elements is useful as an energy absorptionstructure, as by interposition of the layer of stacked, corrugatedelements between relatively movable components 46 and 48. Any tendencyof the components 46 and 48 to move towards one another will create atendency of the stacked elements to distort by bending and by sliding onone another, thereby more closely nesting together.

If the elements are made of a resilient material such as spring steelthat will bend without permanent deformation, then the plurality ofstacked elements will act like a spring, the corrugations nestingtogether under the force imposed by the components 46 and 48 movingtogether, but springing back essentially into their originalconfiguration upon release of such force as the components 46 and 48move apart. If the elements are made from a material that willpermanently deform under such force, as for example soft aluminum orcopper, then the plurality of stacked elements absorb the energy uponbeing compressed by the relative movement of components 46 and 48.

It is apparent, then, that the plurality of stacked elements can be madeto work like a compression spring with little energy absorbed, or as anenergy absorber with appreciable energy absorbed, or intermediately,depending upon the materials of construction and upon such factors asthe size of the corrugations, the thickness of the elements, thestiffness of the element material, etc. The character of these and otherparameters may therefore be selected to fit the particular application.Accordingly, the term energy absorber, absorber, or spring, as usedherein, is to be construed as comprehending both springs and energyabsorbers, as well as combinations thereof.

The elements He and 14e as seen in FIG. 12 are characterized by roundednodes 50 rather than sharply angular nodes, as in FIG. 3, for example.While a rounded node is a preferred shape to facilitate bending andsliding of the elements on one another while the assembly 8 acts as anenergy absorber, it is not critical that the nodes be rounded. Sharpangular nodes might be preferred in certain materials or for certainapplications, such as to vary the coefficient of friction duringrelative sliding of the elements.

Referring now to FIGS. 17 and 18, there is illustrated another structureaccording to the invention, in which ductile or permanently deformableelements 52 and 54 are interleaved between each pair of corrugatedelements 12e and 14e. In this embodiment, the elements 122 and 14e areresilient so as to return essentially to their original corrugated shapeupon movement apart of the components 46 and 48. FIG. 17 shows theassembly loosely positioned between the relatively movable components.FIG. 18 shows a representative pair of the elements 122 and 142 moredeeply internested under the force developed by the components 46 and 48moving closer to gether, with the interleaved elements 52 and 54stretched to conform to the new geometrical pattern, and with resultingenergy absorption by the assembly. The structure will continue to absorbenergy until the interleaved elements fail or until completeinternesting has been achieved, whichever occurs first. Upon subsequentloadings by the relatively movable components, even if the interleavedelements have been broken, the structure will continue to act like acompression spring. Furthermore, the structure may be reset to again actas an energy absorber merely by removing the stretched elements 52 and54 and replacing them with new ones of the original contour. It may bedesirable with certain materials to attach elements 52 and 54 toelements 122 and 14e at points 56, as by suitable adhesives or bywelding, for instance, to prevent sliding of the interleaved elements.However, the tendency under load of the interleaved elements to lock atthe junctures of the nodes 50 and the long sections 18e will generallymake this attachment unnecessary.

Referring now to FIG. 19, an embodiment of the invention is illustratedwhich is essentially identical to the embodiment of FIG. 12, except forcertain nodal attachments. More particularly, if alternate nodes 50 ofeach element 12a and 14e are attached to the long sections 18s of eachelement 122 and 14e at points 58 in the plurality of stacked elements,with the remaining nodes left unattached at'their junctures with thelong sections 18 e, the structure still acts like a spring or an energyabsorber in essentially the same manner as though all nodes are leftunattached as in FIG. 12. However, the nodal attachments 58 are usefulin holding the entire structure together, as for example for handlingpurposes, greatly facilitating the practical use of the invention forcertain applications. The points of attachment at 58 are merelyexemplary, and other points of attachment may be utilized if desired, solong'as the attachment points are chosen such as to cause no undueimpairment of the ability of the stacked elements to compress into oneanother under load from the relatively movable components 46 and 48.

FIG. 20 illustrates yet another embodiment of the invention adapted foruse as an energy absorbing structure. Because certain configurations ofmovable components 46 and 48 may not have fiat faces as depicted, itwould be preferable in such a case to provide a means for spanning andreinforcing the outer corrugations or nodes '50 of the plurality ofstacked elements. Accordingly, an undulating or wave-like element 60 isnested in the corrugations of the outer element 12e to providereinforcement, and a straight element 62 is assemblednext to the element60 for further reinforcement and to further insure uniform loaddistribution into the energy absorbing structure. This structure isuseful, for example, where the energy absorbing structure is a boat slipbumper. The movable element 46 in that case would be the bow of theboat, and the existence of the straight element 62 prevents the bow fromlocking into the corrugations of the structure and tearing it apart.

Elements 60 and 62 may either be attached to the outside element, inthis case the element 12a, or to each other, or left partially orentirely unattached, as desired, depending on the application ofinterest. Either or both elements 60 and 62 may be attached Withoutappreciably changing the total deflection characteristics of theassembly, although a somewhat different distortion of the nestedcorrugations occurs because of the restraint of the attachedcorrugations against the slight sidewise movement they want to undergo.

FIG. 21 illustrates the manner in which the elements 12a and 14a of FIG.12 may be nested to facilitate storage, shipment, and handling. Themiddle element Me of those illustrated is simply reversed in position topermit such nesting.

Another embodiment of the invention is illustrated in FIG. 22. Thisshows a variation in the manner of arranging the plurality of stackedelements 12e and 14a to create, for example, a graded or strongerstructure. In this case two or three of the elements 14 and 12e arenested together for additional strength. If desired, one or more ofthese additional elements may be made of a material such that itfunctions in a manner similar to that of the element 52 of theembodiments of FIG. 17 or 18. It will be apparent that the elements maybe thus nested in any of a large number of combinations, permitting theconstruction of a variety of springs and energy absorbers by differentlyarranging a series of identical elements. Dissimilar elements may alsobe made to nest in this manner, permitting the fabrication of a stillgreater variety of structures.

Referring now to FIG. 13, there is illustrated yet another cellulararrangement according to the invention, in which the first elements 12are characterized by short sections 167 which are of the same lengththroughout the length of the element 12 but the long sections 18 areprogressively longer in one direction. Likewise, the second elements 14are similarly configured with the short sections being of equaldimension to one another, but with the long sections being ofincreasingly greater length to the right, as viewed in FIG. 13. This isuseful in certain applications because it produces cells of increasingsize in a longitudinal direction. The structure is also useful indecorative applications where the dissimilar cell size is aestheticallyattractive.

Referring to FIG. 14, there is illustrated yet another cell arrayaccording to the invention, the particular array shown beingcharacterized by alternate first elements 12g having sections 16g and18g of equal length. However, it is important to note that the secondelements 14g include the characteristic long and short sections. Thiscell array is illustrative of the fact that the generally triangularcell configuration of the present invention is achleved with juxtaposedcorrugated elements so long as at least alternate ones of the elements,in this case the elements 14g, are characterized by long and shortsections between the nodes.

FIG. 15 is illustrative of a structure in which the alternate elements1211 and 1411 are inclined in two directions relative to one another.For example, the cell array of FIG. '2 is characterized by cell wallswhich all lie in planes which are perpendicular to the plane of thepaper on which FIG. 2 is drawn. In contrast, the cell walls of theelements 12h and 14h are inclined with respect to such plane. Thisproduces an offset relationship between the elements at the nodal areas,as best viewed in FIG. 16, assuming that the elements 12h and 14h are ofuniform depth throughout their length. The cellular array of FIGS. 15and 16 is particularly adapted for decorative applications.

Summarizing the foregoing configurations, it will be apparent that eachof the configurations is characterized by a substantially triangularcell, that all of the elements constituting the core array arecorrugated. Moreover, each cell defining the cellular structure ischaracterized by a wall formed by an entire section or leg of acorrugation, and by portions of the legs or sections of two adjoiningcorrugations. The elements may be joined in the form of doublets ortriplets as manufacturing aids, which is particularly important wherethe elements of the structure are made of relatively flimsy material.The shape and size and arrangement of the triangular cells is infinitelyvariable to provide innumerable cell patterns for decorative purposes.The core array is rigid in bending, even without the use of facing orsandwich skins, because of the truss-like structure created by thetriangular configuration. The elements can also be assembled inun'bonded relation for use as energy absorbers. Of particular importancein all of the foregoing structures is the arrangement of the alternateelements such that they tend to interengage and automatically positiontheir nodes into correct alignment, without resort to internal mandrelsor the like. This positioning or alignment can be maintained relativelyeasily, as previously described, so that it is possible to provide awelded or brazed connection at each of the nodes without having toutilize any secondary tooling or internal mandrels. In addition, each ofthe elements can be made of decreasing height from one end to the otherso that the assembled elements will form a tapered structure. Such astructure is useful, for example, as a truss-like structure which can beused in conjunction with facing skins attached to the outermostcorrugation nodes to provide a tapered structure panel. Various tapers,undulations, compound forms and the like can thus be provided simply byutilizing elements of appropriate dimensions and configurations.

Where the core arrays of FIGS. 2, 4, 5, 6, 10 or 13 are used, thestructures are rigid in all directions because the nodes meet on eachside of an intervening element. Where this is not the case, as in FIG.7, the structure can be squeezed or collapsed to a certain extent,although it will not sag when spanning an area.

In view of the fact that the nodes of the elements 12 and 14 may beeither sharply angular, rounded, or flattened, the term node as used inthe appended claims is to be construed as comprehending these andanalogous node shapes. Likewise, the term sections used in the claimscomprehends the internodal sections between the nodes, whether suchsections be planar, curved, of equal length, smooth, or characterized bya series of smaller or secondary wrinkles or corrugations (not shown)for improved columnar rigidity.

Various modifications and changes may be made with regard to theforegoing detailed description without departing from the spirit of theinvention.

I claim:

1. A cellular structure comprising:

first and second corrugated elements, each of the corrugations of saidelements being defined by a succession of short and long sections whosejunctures define nodes, said long sections of said first element beingsimilarly directionally oriented, said second element being arrangedoppositely of said first element with said long sections of said secondelement being directionally oriented similarly to one another butgenerally transversely of the directional orientation of said longsections of said first element whereby alternate ones of said nodes ofeach said second element engage successive ones of said long sections ofthe adjacent said first element, and alternate ones of said nodes ofsaid adjacent first element engage successive ones of said long sectionsof said second element, thereby to form a plurality of cells eachdefined by one of said short sections, and by portions of a pair ofadjacent said long sections of said first and second elements; and

means maintaining said first and second elements in engaged relation.

2. A cellular structure according to claim 1 wherein only a single saidfirst element and a single said second 1 1 element are in engagedrelation, said alternate ones of said nodes of said second element beingsecured to said first element and said alternate ones of said nodes ofsaid first element being secured to said second element to constrainsaid elements against movement relative to one another.

3. A cellular structure comprising a plurality of indi- 'vidualstructures according to claim 2, said individual structures beingsimilarly directionally oriented and secured together at the nodesthereof to form an array of closed cells.

4. A cellular structure according to claim 1 wherein each said shortsection is generally planar, dimensionally identical, and substantiallyperpendicular to an imaginary plane passing through alternate nodes ofthe associated one of said elements.

5. A cellular structure according to claim 4 wherein each said longsection is generally planar, dimensionally identical, and intersects theplane of the adjacent said short section at an included angle ofapproximately sixty degrees.

6. A cellular structure according to claim 4 wherein each said longsection is generally planar, dimensionally identical, and intersects theplane of the adjacent said short section at an. included angle ofapproximately forty-five degrees.

7. A cellular structure according to claim 1 wherein each said shortsection is generally planar, dimensionally identical, and intersects atan angle of approximately sixty degrees an imaginary plane passingthrough alternate nodes of the associated one of said elements; andwherein each said long section is generally planar, dimensionallyidentical, and intersects the plane of the adjacent said short sectionat an included angle of approximately ninety degrees.

8. A cellular structure according to claim 1 wherein .the dimensions ofsaid long and short sections of said first element are different fromthat of said second element.

9. A cellular structure according to claim 1 wherein each of said nodesis defined by a relatively-sharp bend whereby engagement of said nodewith the adjacent said long section provides line contact. A a

10. A cellular structure according to claim 1 wherein each of said nodesis flattened to define a planar section whereby engagement of said nodewith the adjacent said long section provides area contact,

11. A cellular structure according to claim 1 wherein each of said nodesis curvilinear whereby each of said elements is characterized by anundulating, wave-like form. i

-12. A cellular structure according to claim 1 wherein each of saidelements is characterized by a sawtooth pattern whereby each of saidcells is triangular in configuration.

References Cited UNITED STATES PATENTS 2,020,639 11/1935 Grayson et al,161-135 X 3,041,223 '6/1962' Sage 161-135 X 3,168,432 2/1965 Elfving161-136 X 3,432,859 3/1969 Jordan et al. 161-136 X JOHN T. GOOLKASIAN,Primary .Examiner H. F. 'EPSTEIN, Assistant Examiner I U.S. Cl. X.R.

161-135, 137; 206-46 FR; 229-14 C UNITED STATES PATENT OFFICE UEHFICATE9F EQ HQN Patent No. 3,669,820 Dated August 1972 In ent r( K. It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 3, lines 41 and 42, cancel "and therefore 7 can be made to spanrelatively large areas." and insert Y the undesired weight of doublewalls in the nodal areas.

Column 6; line 74, cancelT'section'F and insert sections 4 Signed andsealedv this 19th day of December 1972.

(SEAL) Attest:

EDWARD M..FLETCHER,JR. ROBERT GO'I'TSCHALK Attesting OfficerCommissioner of Patents FORM PO-lOSO (10-69) USCOMM-DC 60376-P69 r usGOVERNMENT PRINTING OFFICE: I969 0-366-334,

